<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box {
      width: 200px;
      height: 200px;
      background-color: red;
    }

    @media screen and (max-width:1000px) {
      .box {
        width: 100px;
        height: 100px;
        background-color: blue;
      }

    }
  </style>
</head>

<body>
  <div class="box">
    daidhis
  </div>
</body>

</html>